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It would really be a nice feature to have recorded annunciations. If it takes 6 hours to fill a tank, a loudspeaker saying Tank Is Full, or Warning Too Hot or the like. An alarm beeper does not tell anything about the condition.

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There are always a few ways to kill that damn cat. Much of my work is what you could call "mechanical animation". So I have been working with sound files matched to plcs since the year dot. Ages ago I thought it was great when I could have CDs running concurrently with actions, instead of cartridge tape players that I'd used up till then! As tech progressed so did my methods. But I have always kept the KISS combined with the "cheap but very effective" principle in mind.

If you don't have a need for the sound file to play immediately, (and it looks like a delay of up to a minute might be ok in your situation) then you can get by quite easily by having a simple SD card player with one sound file on the card containing all your messages laid out sequentially with a small bit of silence b/n them. You simply start the player running, and time your method of "speaker output volume adjustment" to turn on when the "time zone" of the relevant message is current. You can then do a simple repeat by restarting the player and doing it all again. So the longest delay is the total length of the sound file. You obviously put your "most demanded, on time" messages as the first ones in the file.

You can also get little modules that react to switched inputs to play certain sound bites.

With any of this, you have to be prepared to do a little hardware tinkering/mods/soldering....but it isn't rocket science!

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And some more info. For systems that need to run different versions at a certain time, like on the 1/4 hour etc, I prestart the sound system before the required time, so that the player has progressed through to the correct sound sequence at the matching time. Some of my files are >10 minutes, with many different sound files.

Using the little modules, individual file addressing works fine in theory via more complex interfacing, but I have had issues with the sound system easily confused as to where it is. Remember that these things need to work gliche free without any human help 24/7. The single sound file system above has worked best, because it always starts from a known point. And it is really easy to put together and maintain, needing no fancy hardware apart from 2 or 3 outputs, and is essentially dirt cheap. The players are much like this sort of thing...Google Kentiger HY-502.

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The LTM38A looks to be a very useful device. Every so often I cruise google seeing if something more suitable has surfaced, but I've missed this one. That's the nature of web surfing...it might be miles down in the pack when you look, and if you don't know it's name you're stuffed.

I particularly like that the serial interface returns what it has been asked to play...a good way to check. And it is stereo. And is an amp.

I wouldn't be using the relay(ed) versions because I don't need them and sometimes with the systems you have to be careful in volume control/speaker setup to avoid startup/shutdown thumps. Not good for speakers. The relays on the thing look like they can only be triggered to come on concurrently with the designated file playing. But for your instance, Visco, the ability to perhaps switch different speakers around the installation might be a good thing. One sound device does messages for all plcs and locations? And I'm sure the device has been made to alleviate speaker issues doing just this situation....that's what it appears to have been built for. I know that there are two conflicting opinions in this paragraph!!! Pros and Cons both ways!

So.... I would seriously consider it for my next project. The serial control wouldn't be that hard to set up, and the "file on demand" principle would be good and make things a lot easier on more complex installs.

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kratmel, I used something like this ages ago and it worked fine in the instance because 8 lots of "speaking" weren't very long and only needed to be mono. The time limit and mono on this style can be an issue in my situations.

Visco, how are you planning to trigger things? Serial or multiplex the inputs? If you aren't going to do serial, I'd look at putting on an IO-RO8 as the simplest method given the voltages being switched. In some ways this will be a lot simpler than serial. However, consider that my issues with multiplexing inputs in the past all related to the various modules not being able to handle switch "delays and bounce" adequately, resulting in wrong things being interpreted into the controlling chip due to miniscule variations in timing. That's why I really like the serial system, for better accuracy in the send from the plc, and also sending confirmation back. But also, perhaps this unit can tolerate switch systems better....I haven't fully gone through the manual, only a skim, so maybe there is a setting for input times that would solve all my previous issues.